The invention concerns a tensioner for a power transmission belt.
It is known that the transmission of power from one shaft to another using a belt, such as is used in automobiles, trucks, agricultural machines or other types of machines requires the presence of a belt tensioning device to ensure proper functioning. Indeed, any sliding of the belt with respect to the pulleys with which it co-operates inhibits the transmission of movement. Such sliding can arise from a natural stretching of the belt with use, or from differences in dimensions between belts, or from slackening in the belt tension, at the starting of the drive motor for example.
Furthermore, it is important in a power transmission system that the functioning is as regular as possible and, to this end, means are provided for damping the vibrations generated in the belt by the periodic irregularities in the motor speed, in particular during the deceleration, or on account of the jolts occuring at the starting up or stopping of the equipment integral with the shafts driven by the belt.
To satisfy the above conditions transmission belt systems have been fitted with a roller co-operating with the belt and with an axis moveable along the longitudinal length of a return spring, such a device being called a linear tensioner. The damping of vibrations is carried out by a damper, separate from the spring, usually of the hydraulic or boundary friction type and thereby attenuating the phenomenon of resonance of the tensioner spring.
In such a device, for example WO-83/00731, the spring comprises a stack of Belleville washers, and the hydraulic damper is a piston system separate from these washers, with a valve in parallel on the piston cylinder, such that the roller deflecting assembly is both heavy and cumbersome.